1. Field of the Invention
The invention relates to an exhaust gas control apparatus of an internal combustion engine.
2. Description of Related Art
One known exhaust gas control apparatus of an internal combustion engine has a particulate filter for trapping particulate matter in exhaust gas, arranged in an engine exhaust passage. The exhaust gas control apparatus calculates an estimated trapped amount that is an estimated value of the amount of particulate matter trapped in the particulate filter, based on an operating state of the internal combustion engine, and when this estimated trapped amount exceeds a predetermined upper limit amount, the exhaust gas control apparatus performs temperature increase control that increases the temperature of the particulate filter to remove the particulate matter from the particulate filter.
However, the estimated trapped amount does not necessarily accurately represent the actual amount of trapped particulate matter. If the estimated trapped amount is less than the actual amount of trapped particulate matter, the temperature increase control will not be started even if the actual amount of trapped particulate matter exceeds the upper limit amount, so pressure loss of the particulate filter may become excessively large. On the other hand, if the estimated trapped amount is greater than the actual amount of trapped particulate material, the temperature increase control will be executed before the actual amount of trapped particulate material exceeds the upper limit amount, and as a result, the temperature increase control may be executed too frequently.
Therefore, an exhaust gas control apparatus of an internal combustion engine described in Japanese Patent Application Publication No. 2005-155500 (JP 2005-155500 A) is designed to detect a rate of increase in the temperature of the particulate filter while the engine is decelerating while temperature increase control is being performed, and correct the estimated trapped amount based on this temperature increase rate. More specifically, when the temperature increase rate is small, the estimated trapped amount is decrease-corrected, and when the temperature increase rate is large, the estimated trapped amount is increase-corrected.
However, the rate of increase in the temperature of the particulate filter when the temperature increase control is performed relies not only on the amount of trapped particulate matter when the temperature increase control starts, but also on the amount and temperature of exhaust gas that flows into the particulate filter while the temperature increase control is being performed, for example. More specifically, for example, when the amount of exhaust gas that flows into the particulate filter is large, the amount of heat removed from the particulate filter by the exhaust gas is large, so the temperature increase rate is smaller. In this case, even if the actual amount of trapped particulate matter is larger than the estimated trapped amount, the estimated trapped amount may be decrease-corrected. That is, in JP 2005-155500 A, the amount of heat removed from the particulate filter by the exhaust gas is not accurately ascertained, so the estimated trapped amount is not always able to be accurately corrected or calculated.